Historically, the commercial production of ethylbenzene was dominated by liquid-phase aluminum chloride catalyzed processes until the early 1980s when the first vapor-phase zeolite-based process was introduced. The zeolite vapor-phase technology subsequently achieved commercial success because it proved to be more efficient and avoided the difficulty of handling aluminum chloride. However, vapor-phase processes operate at high temperatures and produce considerable by-products. While improvements were made over the years, it was not until the arrival of liquid-phase processing in the early 1990s that zeolite-based technologies could produce a high-purity ethylbenzene product.
More specifically, to produce ethylbenzene, polymer grade ethylene can be reacted with benzene that is in stoichiometric excess under liquid-phase conditions in a fixed-bed, multi-stage alkylation reactor. Ethylene conversion is essentially complete, with selectivity to ethylbenzene in the alkylation reaction at over 90%. Unreacted benzene is then separated and recycled back to the reaction section. Ethylbenzene product is recovered from polyethylbenzenes. Polyethylbenzene is then fed to a fixed-bed transalkylation reactor and converted into additional ethylbenzene product by reacting with excess benzene. The molar yield of ethylbenzene for the overall process can exceed 99.5% relative to both ethylene and benzene. However, the non-molar yield of 0.5 percent can include trace compounds such as sodium, calcium, potassium, chlorine, iron, titanium, sulfur and zinc that can result in undesired byproducts.
Cumene is an important intermediate in the chemical and polymer industries, with global cumene production currently exceeding twelve million metric tons annually. Cumene is generally produced by the alkylation of benzene with a C3 alkylating age (e.g., propylene) in the presence of an acid catalyst. Early cumene plants used solid phosphoric acid as the catalyst, but more recently most cumene manufacturers have replaced the phosphoric acid with molecular sieve catalysts. Examples of benzene alkylation processes employing molecular sieve catalysts can be found in, for example, U.S. Pat. Nos. 4,185,040; 4,992,606; and 5,073,653.
Processes for production of cumene using molecular sieve or zeolite-based catalysts can be conducted in either the vapor phase or the liquid phase. However, in view of the improved selectivity and decreased capital and operating costs associated with liquid phase operation, many commercial cumene processes now operate under at least partially liquid phase conditions.
The selectivity to the desirable ethylbenzene and cumene is important to the economics of the catalytic transformation of both feed stock and recycle streams for zeolite-based catalysts used in liquid phase alkylation and transalkylation systems. Improvements in selectivity can advance raw material utilization and debottleneck existing processes. For example, ethylbenzene can be produced in very high molar yields under liquid-phase conditions in fixed bed, multi-stage alkylation reactor using zeolite-based catalysts. Yet, certain “non-selective” catalytic sites exist on otherwise “selective” catalyst and result in increased yields of undesirable byproduct during reaction and reduce the selectivity to the desirable products.
A need exists, therefore, for methods that suppress “non-selective” catalyst sites on transalkylation catalysts and cause the non-selective sites on the surface, or within the interior channels, of the catalysts to become inactive so to avoid the production of undesired byproducts and improve selectively of products to be produced.